An alternative to braces includes the use of aligner-type dental appliances for realigning teeth. Such an appliance may be comprised of a thin concave trough of material that forms a receiving cavity geometry that generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth configuration. Placement of the dental appliances over the teeth applies controlled forces in specific locations to gradually move the teeth into a new predetermined configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of predetermined intermediate arrangements along the most effective and efficient treatment path to a final predetermined arrangement.
Some dental appliances are made using polymers, such as thermoplastic polyurethane. Polymers may deform over time and/or use due to external and internal forces. Some deforming external forces may include repeated insertion/removal and biting/wearing. An internal deforming force may include material stress relaxation. The deformation may reduce tooth moving forces, thereby reducing the usefulness of the dental appliance. Once the usefulness of the aligner dental appliance is reduced, the dental appliance is typically disposed of, and either a replacement dental appliance is made or the next dental appliance in the treatment series is used. Hence, the shorter the effective usefulness of the dental appliance, the more frequently the dental appliance needs to be changed. Consequently, an extension of the effective usefulness of the dental appliance is desirable.